The Centre for Health Protection (CHP) of the Department of Health is investigating this evening (August 9) a case of dengue fever (DF) and again urged the public to maintain strict environmental hygiene, mosquito control and personal protective measures both locally and during travel.

"Although the patient had traveled to Vietnam, a DF affected area, in the incubation period, her residence in Prince Edward is in close proximity to the first local case reported on August 7. This case is hence managed as a locally-acquired infection as a precautionary measure," a spokesman for the CHP said.

The female patient, aged 25 with good past health, lives in a unit on Boundary Street, Prince Edward. She has developed fever, headache, muscle pain, retro-orbital pain and skin rash since August 2. She attended a Chinese medicine practitioner on August 3, a private doctor on August 4 and another private doctor on August 7 and 8 when she was referred to Queen Elizabeth Hospital and admitted for management on the same day. She is now afebrile and has been in stable condition.

Initial enquiries revealed that the patient had travelled to Vietnam from July 15 to 23. She works in Central and her local movements before onset were mainly within her workplace and residence. She cannot recall mosquito bites both locally and during travel. Her travel collateral and household contact have remained asymptomatic and been put under medical surveillance.

"As a precautionary measure, we are working closely with the Food and Environmental Hygiene Department (FEHD) to assess and prevent any possible spread of infection. The FEHD's vector investigations, surveillance and control will follow. Epidemiological investigations are ongoing," the spokesman said.

Officers of the CHP have conducted site visit and field investigations by questionnaire surveys at the patient's residence for active case finding and arranging blood tests. A health talk jointly with the FEHD will be arranged to deliver health advice.

Persons who have been to the vicinity of Boundary Street, Prince Edward with DF symptoms should call the CHP's hotline (2125 1133) operating from 9 am to 5.45 pm tomorrow onwards for laboratory investigation or referral as appropriate.

"We have informed the Guangdong and Macau health authorities of the case and will issue letters to local doctors and hospitals to alert them to the latest situation," the spokesman added.

In the rainy season, the public should take heed of the following advice on mosquito control:

Completely change water of flowers and plants at least once a week. The use of saucers should be avoided if possible;

Level irregular ground surfaces before the rainy season;

Avoid staying in shrubby areas; and

Take personal protective measures such as wearing light-coloured long-sleeved clothes and long trousers and apply insect repellent containing DEET to clothing or uncovered areas of the body when doing outdoor activities.

To reduce the risk of infections spread by mosquitoes, apart from general measures, travellers returning from affected areas should apply insect repellent for 14 days (DF) or at least 21 days (Zika Virus Infection) upon arrival in Hong Kong. If feeling unwell, seek medical advice promptly and provide travel details to the doctor. DEET-containing insect repellents are effective and the public should take heed of the tips below:

Read carefully the label instructions first;

Apply right before entering an area with risk of mosquito bites;

Apply on exposed skin and clothing;

Use DEET of up to 30 per cent for pregnant women and up to 10 per cent for children;